OD&D Why is AC 2 the best armor class?

[Nikosandros]

From my understanding (which could be wrong), armor class derived from some naval wargame and is descending because, in OD&D, it is a "static" value which depends only on armor and shield and, thus, it is an indicator in which lower numbers represent a better "class" of armor. This makes sense. With only leather, chain and plate there is no overlap. Why then is the lowest class 2 and not 1? It seems to be that no monsters has an AC lower than 2, so it does not appear to be reserved for natural armor better than plate.

 

[Spectral Anomaly]

Monsters weren't worthy of having first class armor.

 

[Jack Daniel]

I don't know, but if I had to take a guess, it derives from baseline odds of 2 in 6. Lots of things in Chainmail and OD&D happen on 1–2 on 1d6.

If you average together all the saving throw numbers for 1st level characters of all classes, you get 14+ on the d20. That's 35%, pretty darned close to one third.

And the chance of a 1st level player character (THAC0 19) with no exceptional stats or magic to hit the median armor class, chainmail without a shield, AC 5? That also happens on 14+, or about a third of the time.

 

[Nikosandros]

I don't know, but if I had to take a guess, it derives from baseline odds of 2 in 6. Lots of things in Chainmail and OD&D happen on 1–2 on 1d6.

If you average together all the saving throw numbers for 1st level characters of all classes, you get 14+ on the d20. That's 35%, pretty darned close to one third.

And the chance of a 1st level player character (THAC0 19) with no exceptional stats or magic to hit the median armor class, chainmail without a shield, AC 5? That also happens on 14+, or about a third of the time.

Since the to-hit tables are equally arbitrary, they could have shifted the tables and the ACs by 1 and obtained the same odds.